1. Field of the Invention
This invention relates to a multimode ionization device, more particularly to a multimode ionization device adapted for use in a mass spectrometer.
2. Description of the Related Art
A mass spectrometer works by ionizing analytes to generate ionized analytes and measuring their mass-to-charge ratios. There are several approaches for ionizing analytes, and different approaches are suitable for ionization of different classes of analytes. For example, an electrospray ionization device is suitable for ionizing polar molecules (such as peptide, protein, etc.), but not for nonpolar molecules (such as saturated hydrocarbons, polycyclic aromatic hydrocarbons, etc.). An atmospheric pressure chemical ionization device is suitable for ionizing nonpolar molecules, but not polar molecules. Thus, when analyzing a sample including polar and nonpolar molecules, it is necessary to analyze the sample separately using different mass spectrometers with different ionization devices. As such, there is a need to provide a multimode ionization device for ionizing analytes of different properties.
Referring to FIG. 1, U.S. Pat. No. 7,078,681 discloses a multimode ionization source which includes an electrospray ionization source (ESI source) 5 and an atmospheric pressure chemical ionization source (APCI source) 6 that is disposed downstream of the ESI source 5. The ESI source 5 includes a nebulizer 51 and a drying device 52. A liquid medium 50 including analytes is introduced into the nebulizer 51, and is transported to an orifice 511 from which a charged aerosol is produced, moving to an ionization region 70. The drying device 52 has a sweep gas conduit 521 for providing a sweep gas to the charged aerosol at the ionization region 70. A first potential difference between a nebulizer tip 512 of the nebulizer 5 and a first electrode 53 creates an electric field for producing the charged aerosol at the nebulizer tip 512, while a second potential difference between a second electrode 54 and a conduit 8 creates an electric field for directing or guiding ions toward the conduit 8. The APCI source 6 includes a corona needle 61. A corona discharge is produced by a high electric field at the corona needle 61. The electric field is produced predominately by the potential difference between the corona needle 61 and the conduit 8. In this case, when the charged aerosol travels to the ionization region 70, it can be further ionized by virtue of the corona discharge.